Vibrational assignment and structure of 4-amino-3-cyano-3-penten-2-one

Article abstract of DOI:10.1016/S0022-2860(02)00179-5

Fourier transform infrared and Fourier transform Raman spectra of 4-amino-3-cyano-3-penten-2-one and its deuterated analogue have been obtained. Density functional theory (DFT) B3LYP and G96LYP calculations have been carried out with the purpose of understanding the vibrational spectra of this compound and its deuterated analogue. Vibrational wavenumbers calculated by B3LYP/6-31G* (with a p shell added on the amine protons) force field are closed with the experimental results. The percentage of deviation of the bond lengths and bond angles gives a good picture of the normal modes, and serves as a basis for the assignment of the wavenumbers. The calculated geometrical parameters show a strong intramolecular hydrogen bond with a N···O distance of 2.605-2.622 A?. This bond length is about 0.04-0.06 A? shorter than that in its parent, 4-amino-3- penten-2-one (with no cyano substitution in the α-position). Experimental evidences also indicate presence of an intermolecular hydrogen bond in the solid state, completely, and in solution, partially.

Full text of DOI:10.1016/S0022-2860(02)00179-5

Journal of Molecular Structure 613 (2002) 195–208
www.elsevier.com/locate/molstruc
Vibrational assignment and structure of
-amino-3-cyano-3-penten-2-one
4
*
Haydar Raissi, Sayyed Faramarz Tayyari , Fariba Tayyari
Chemistry Department, Ferdowsi University, Mashhad 91774, Iran
Received 3 January 2002; accepted 16 April 2002
Abstract
Fourier transform infrared and Fourier transform Raman spectra of 4-amino-3-cyano-3-penten-2-one and its deuterated
analogue have been obtained. Density functional theory (DFT) B3LYP and G96LYP calculations have been carried out with the
purpose of understanding the vibrational spectra of this compound and its deuterated analogue. Vibrational wavenumbers
p
calculated by B3LYP/6-31G (with a p shell added on the amine protons) force field are closed with the experimental results.
The percentage of deviation of the bond lengths and bond angles gives a good picture of the normal modes, and serves as a basis
for the assignment of the wavenumbers. The calculated geometrical parameters show a strong intramolecular hydrogen bond
˚
˚
with a N· · ·O distance of 2.605–2.622 A. This bond length is about 0.04–0.06 A shorter than that in its parent, 4-amino-3-
penten-2-one (with no cyano substitution in the a-position). Experimental evidences also indicate presence of an intermolecular
hydrogen bond in the solid state, completely, and in solution, partially. q 2002 Elsevier Science B.V. All rights reserved.
Keywords: Intramolecular hydrogen bond; Aminoketone; 4-amino-3-cyano-3-penten-2-one; Vibrational spectra; DFT calculations
1
. Introduction
and Terpinski [9] studied imine–enamine equili-
brium of some b-ketoamines compounds by
using NMR spectroscopy. They considered all
possible structures of these compounds and
showed that structure B in Fig. 1 is the most
stable structure. This fact was confirmed by the
recent experimental and ab initio calculations
Three forms A, B and C are possible for a,
b-unsaturated-b-ketoenamines (see Fig. 1). Ueno
and Martell [1] concluded that a tautomeric
equilibrium exists between the forms correspond-
ing to A and B for bisacetylacetone-ethylene
diimine and related substances. Cromwell [2] has
written an extensive review on the organic
chemistry of b-ketoamines. Holtzclaw et al. [3]
described the synthesis and infrared spectra of
these ligands and their copper derivatives.
Dudeck et al. [4–7], Ostercomp [8], Dabrowski
1
13
15
[
10,11]. Using H, C and N nuclear magnetic
resonance spectroscopy, Tan et al. [12] studied
the tautomerism of 22 b-ketoamines, which may
be regarded as six-membered heterocyclic b-
tricarbonyl and b-pentacarbonyl systems. They
demonstrated the preference of the keto-amine,
B, to the enol-imine, C, and suggested that this
should be due to the stronger intramolecular
hydrogen bond in the NH· · ·O system than in the
N· · ·HO system. Hansen et al. [13] examined
*
Corresponding author. Tel.: þ98-511-8438032; fax: þ98-511-
780216.
E-mail address: tayyari@ferdowsi.um.ac.ir (S.F. Tayyari).
8
0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(02)00179-5

196
H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
Fig. 1. Tautomery in b-ketoenamines.
1
3
deuterium isotope effects on C NMR chemical
shifts on the some other six-membered hetero-
cyclic b-ketoamines. On the other hand, the N–
H· · ·O hydrogen bonds are ubiquitous in biologi-
cal systems such as DNA, base pairs, proteins
and ligand receptor interaction [14–16]. Further-
more, the aminoketone compounds show anti-
depressant activity [17].
replaces the H atom in position a (position 3 in Fig.
2) [18–20]. The hydrogen bond becomes stronger
when bulky groups are involved [21–25]. By
analyzing the substitution effect of simple substitutes
such as cyano group, an electron withdrawing moiety
with the least steric effect on the structure, it is
possible to study the mesomeric effect for this kind of
substitution with negligible interference of the steric
effect. Yet, the effect of substitution in a position of
ketoenamines has been investigated neither
experimentally nor theoretically as extensively as
b-diketones.
The ketoenamine, form B, of a, b-unsaturated-b-
ketoenamines are stabilized by an intramolecular
hydrogen bond [10,11]. This hydrogen bond for-
mation leads to an enhancement of the resonance
conjugation of the p-electrons, which causes a
marked tendency for equalization of the bond order
of valence bonds in the resulting six-member chelated
ring. Therefore, it seems that any parameter that
affects the electron density of the chelated ring will
change the hydrogen bond strength. It seems that
substitution in a or b position drastically changes the
hydrogen bond strength, the same as b-diketones [11,
A crystalline derivative of 4-amino-3-penten-2-
0
one (RyH, R yCH
4-amino-3-cyano-3-penten-2-one (RyCN, R yCH
in Fig. 1, hereafter APO) is
0
3
in
3
Fig. 1, hereafter CNAPO). The solubility of this
compound is low and crystallized spontaneously
during preparation. The importance of consideration
CNAPO is because of some resemblance to the
reactions exhibited by the 5-substituted cytosine
residues found in the DNA of the T-even bactrio-
phages [26]. Wierzchowski et al. [27] have reported
the preparation of CNAPO as intermediate in photo-
chemical synthesis of a-cyanoacetylacetone. How-
ever, no spectroscopic data has been reported for this
compound yet.
1
8–20]. In the case of b-diketones, several exper-
imental data suggests that strength of such a bridge
enhances when an electron withdrawing group
The aim of the present paper is to predict the
structure and vibrational spectra (harmonic wave-
numbers, and relative intensities for Raman and IR
spectra) of CNAPO by means of density functional
theory (DFT) levels. Comparing of CNAPO and APO
geometrical parameters gives a clear understanding of
substitution effects of hydrogen atom with cyano
group (in a position) on structure and hydrogen bond
strength of the system. The calculated harmonic force
Fig. 2. View of CNAPO showing the atomic numbering scheme
used in the text.

H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
197
Table 1
Comparison of theoretical geometric parameters of CNAPO and APO at different levels of theory
CNAPO
APO
pa
p p
p
pa
p p
p
B3LYP/6-31G
B3LYP/6-311þþG
G96LYP/6-31G
B3LYP/6-31G
B3LYP/6-311þþG
G96LYP/6-31G
Bond lengths
C
C
C
C
C
C
C
C
2
3
2
4
4
2
3
6
–C
–C
3
4
1.466
1.400
1.241
1.336
1.516
1.506
1.424
1.167
1.024
1.007
1.794
2.610
1.464
1.398
1.236
1.335
1.512
1.503
1.420
1.159
1.020
1.005
1.828
2.622
1.474
1.414
1.255
1.345
1.525
1.514
1.427
1.179
1.037
1.014
1.756
2.605
1.443
1.379
1.246
1.349
1.523
1.507
–
1.442
1.378
1.242
1.347
1.519
1.505
–
1.449
1.391
1.261
1.358
1.576
1.535
–
–O
–N
7
8
–C
–C
–C
5
1
6
–N17
–H
–H10
–
–
–
N
N
O
N
8
8
7
8
9
1.021
1.006
1.858
2.658
1.017
1.004
1.881
2.662
1.032
1.015
1.848
2.669
· · ·H
· · ·O
9
7
Bond angels
C
C
C
C
C
C
C
C
4
2
3
5
3
3
5
1
C
C
C
C
C
C
C
C
3
3
2
4
2
4
4
2
C
C
C
C
2
6
1
3
121.9
122.3
119.5
118.2
121.2
121.6
121.3
117.5
120.2
31.2
121.6
119.3
118.5
122.4
121.8
120.2
117.4
119.6
27.8
122.7
–
123.0
–
123.0
–
119.0
118.2
122.3
121.9
120.9
116.7
119.9
29.7
117.4
121.7
123.4
121.9
116.4
119.2
30.9
118.3
121.6
123.1
122.1
116.3
118.6
32.2
117.5
122.0
123.4
121.3
116.7
119.1
29.9
O
N
N
O
7
8
8
7
H
N
H
9
N
8
H
9
N
8
9
8
O
O
H
7
7
133.8
132.0
122.0
120.7
117.3
136.2
123.5
121.0
115.5
132.6
122.6
121.3
116.1
131.1
121.8
121.2
117.0
133.8
122.6
121.8
115.6
10 122.7
C
C
4
N
N
8
H
H
10
120.8
116.5
4
8
9
a
A p shell ða ¼ 1:1Þ added on the amine protons.
constants of CNAPO were used for predicting the
Raman and IR spectra of deuterated species. The
calculated vibrational frequencies are compared with
the obtained experimental results.
The amount of 12.5 g (0.1 mol) of CNAA was
3
dissolved in 60 cm ammonia solution 25%, refluxed
for 2 h and then stirred continuously for 24 h at room
temperature. Mixture was extracted (3 £ 100 ml) with
chloroform. Organic layer was dried using anhydrous
Na SO , filtered and evaporated under reduced
2
4
2
. Experimental
pressure. The crude product was crystallized from
CHCl . Yield 7.25 g (58%) of colourless crystals; mp
3
1
Acetylacetone and all solvents were purchased
from Fluka. Chloroform and deuterated chloroform
˚
were stored over 3 A molecular sieves.
58 8C, H NMR (CDCl
(s, 3H, CH
3
3
): d 2.28 (s, 3H, CH
); d 6.68(s, 1H, NH free); and d 10.71(s,
1H, NH bonded). The elemental analysis was correct.
Solution of D CNAPO (deuteration done on amine
protons) was prepared by shaking solutions of
CNAPO in CHCl with D O for period of up to
3
); d 2.33
1
The concentration of the samples for H NMR and
2
2
3
FTIR measurements was 0.1 mol dm
.
a-cyanoacetylacetone (hereafter, CNAA) was
synthesized by the Fackler and Cotton method [28].
CNAPO was synthesized by the modification of the
method given for APO in Ref. [29].
3
2
24 h. However, the crystalline D CNAPO was pre-
2
pared from CHCl solution of D CNAPO which was
3
2
dried over anhydrous Na SO followed by removing
2
4

198
H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
p
Fig. 3. Conformations of CNAPO optimized at B3LYP/6-31G level with augmented a p function on the amine protons.
the organic layer under reduce pressure in an
especially designed apparatus [30].
The Infrared spectra were taken on a Shimadzu
theory. This level of theory is an often used
compromise between reliability [20] and economy
of calculations.
4
300 spectrometer. The Raman spectra were collected
The assignment of the experimental frequencies
are based on the observed band frequencies and
intensity changes in the infrared and Raman spectra of
the deuterated species confirmed by establishing one
to one correlation between observed and theoretically
calculated frequencies.
employing a 1808 back scattering geometry and a
Bomem MB-154 Fourier Transform Raman
spectrometer.
The Raman spectrometer was equipped with a
ZnSe beam splitter and a TE cooled InGaAs detector.
Rayleigh filtering was afforded by a set of two
Holographic technology filters. Laser power at the
sample was 40 mw.
4. Results and discussions
The NMR spectra were obtained on a FT-NMR,
Brucker Aspect 3000 spectrometer at 100 MHz
frequency in CDCl at 22 8C and TMS as internal
4.1. Molecular geometry
3
standard.
The full-optimized geometries of CNAPO and
APO are summarized in Table 1 and the geometry of
CNAPO and the numbering of the atoms is given in
Fig. 2. As it is obvious from Table 1, the main effect of
a-cyano substitution is shortening of the N· · ·O
distance and lengthening of the N–H bond length,
compared with the corresponding values for APO.
Calculations at all DFT levels predict that the N· · ·O
3
. Method of analysis
The GAUSSIAN 98W program suite [31] was used
for all quantum chemistry computations. The full
geometry optimization were performed at B3LYP
p
˚
distance in CNAPO is about 0.04–0.064 A shorter
level [32,33] with 6-31G (a p shell, a ¼ 1:1; added
pp
on the amine protons) and 6-311þþG basis sets
than that in APO. These structural changes in CNAPO
suggest a stronger hydrogen bond in CNAPO than that
in APO. This conclusion is consistent with the NMR
proton chemical shift of 9.7 and 10.71 ppm for the
p
and G96LYP level [34] with 6-31G basis set. The
vibrational frequencies were calculated at B3LYP/6-
3
p
1G (a p shell added on the amine protons) level of

H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
199
Table 2
The energies and dihedral angles (8) of CNAPO conformers given in Fig. 3
1
2
3
4
5
N
N
N
O
O
O
8
8
8
7
7
7
C
C
C
C
C
C
4
4
4
2
2
2
C
C
C
C
C
C
5
5
5
1
1
1
H
H
H
H
H
H
11
12
13
14
15
16
164.1
42.7
180.0
59.2
0.0
0.0
180.0
59.2
121.0
121.0
276.1
0.0
259.2
0.0
2121.0
0.0
2121.0
180.0
259.2
180.0
58.0
120.6
120.8
120.8
58.0
2120.1
2418.186810376
2120.7
2418.18679854
7.4
2120.8
2418.18671244
61.4
258.0
2418.18589792
573
258.0
2418.18582405
619
Energy (a.u.)
Relative to 1 (cal/mol)
0
hydrogen bonded proton in APO and CNAPO,
respectively. Table 1 also shows that upon cyano
substitution on a-position both C–C and CyC bond
lengths in the chelated ring are increased, whereas
CyO and C–N bond lengths are decreased. These
behaviours are very similar to those observed for CN
substitution in a-position of acetylacetone [20]. The
bond length increment in CyC could be attributed to
the presence of p-electron delocalization through
NxC–CyC fragment of the molecule, which reduces
its double bond character. The bond length increment
in C–C could be attributed to the reduced electron
delocalization in the OyC–C fragment of the chelated
ring, which increases its single bond character. This
interpretation also accounts for shortening of CyO
bond length. Reduction in the C–N bond length could
be well described by considering increased p-electron
delocalization in the C–N side due to the effect of the
NxC group. The electron withdrawing character of
the NxC group lowers the electron charge density on
the oxygen and nitrogen atoms, which in turn causes
the amine protons to be more acidic and increase both
the inter and intramolecular hydrogen bond strength.
An interesting point, which is noteworthy, is the
planarity of the chelated ring in CNAPO (the same as
APO) which is caused by the formation of a strong
intramolecular hydrogen bond and p-electron conju-
gation in the chelated ring. According to all
bond length in tertiary amides (where hydrogen
˚
bonding is impossible), 1.336 A [35].
The conformation of methyl groups with respect to
the plane of the molecule and with respect to each
other are shown in Fig. 3. The energy values and
dihedral angles of these conformers are listed in Table
2. The dihedral angle f (H11C C N ) at the most
1 5 4 8
stable conformation (1) is 164.18, which is only 7 and
61 cal/mol more stable than the staggered (2) and
eclipsed (3) conformers, respectively. The CH
3
attached to the carbonyl group is eclipsed with respect
to oxygen atom. The calculated barrier to rotation for
this group is about 0.6 kcal/mol, which is about twice
of the corresponding value (0.293 kcal/mol) in
acetylacetone [36].
4.2. Vibrational analysis
The infrared and Raman spectra of CNAPO and
D CNAPO in the solid phase are shown in Figs. 4 and
2
5, respectively. Lorentzian function has been utilized
for deconvolution of the IR spectra of CNAPO in the
2
1
solid phase in 3500–2500 cm region and deconvo-
luted spectrum is shown in Fig. 6. The infrared and
Raman band frequencies for CNAPO and D CNAPO
2
in the solid phase and in CHCl solution along with
3
the calculated frequencies and their assignments are
given in Tables 3 and 4, respectively. Some of the
very important normal modes of the chelated ring are
shown in Fig. 7. The Cartesian representation of the
normal modes, in the absence of potential energy
distribution (PED), permits in the quantum mechanic
ab initio DFT method, to study the distorted geometry
of each mode [37].
calculations, both hydrogen atoms of NH group are
2
completely in the plane of the chelated ring. This
implies that the electron loan pair of the nitrogen atom
is almost completely takes part in the p-electron
delocalization of the chelated ring. This can explain
that why the C–N bond length of CNAPO has not
been shortened compared with the corresponding
The calculated frequencies are slightly higher than

200
H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
2
Fig. 4. Infrared spectra of CNAPO (—) and D CNAPO (- - -).
the observed values for the majority of the normal
modes. Two factors may be responsible for the
discrepancies between the experimental and com-
In the infrared and Raman spectra of CNAPO in
the solid phase two bands were observed at 3340 and
2
1
3161 cm . Upon deuteration, these two bands
disappear and two new bands appear at about 2490
puted spectra of CNAPO and D CNAPO. The first is
2
2
1
caused by the environment. The second reason for
these discrepancies is the fact that the experimental
value is an anharmonic frequency while the calculated
value is a harmonic frequency.
and 2330 cm . According to the theoretical calcu-
lations, we assign these two bands mainly to N–H10
(involved in an intermolecular hydrogen bond) and
N–H (involved in an intramolecular hydrogen bond)
9
stretching, respectively. The corresponding bands for
21
2
.2.1. 3600–1700 cm region
1
4
APO are observed at about 3353 and 3179 cm
,
In this region C–H stretching of the CH3
respectively [11]. Lower band frequency shifts of both
NH stretching modes of NH group in CNAPO in
groups, CxN stretching and the NH/ND stretching
are expected to be observed. The amino com-
pounds show the NH asymmetrical and symmetrical
stretching bands at 3520–3420 and 3420–
2
comparison with those for APO suggest stronger inter
and intramolecular hydrogen bond in CNAPO in
comparison with those in APO. These observations
are consistent with the NMR chemical shift and
calculated bond lengths. The IR spectrum of CNAPO
2
1
3
325 cm , respectively [38]. However, the existence
of intramolecular hydrogen bond perturbs this
pattern [11,39].
in CHCl solution in this region shows three bands at
3

H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
201
2
Fig. 5. Raman spectra of CNAPO (—) and D CNAPO (- - -).
2
530, 3362 and 3171 cm . Two bands, at 3530 and
1
3
analogue clearly shows three bands at 3023, 2975 and
21
2930 cm , which are very closed to the correspond-
2
362 cm , were strongly affected by dilution. The
1
3
band at 3530 cm
2
1
21
(at about 2580 cm
D CNAPO), which its intensity increases on dilution,
in
ing bands observed in the Raman spectrum of
acetylacetone and APO [36,11] and therefore assigned
2
2
1
is attributed to the free NH stretching. The 3362 cm
band, which on dilution shows a decrease in intensity,
to the CH stretching modes. Furthermore, deconvo-
3
lution of the infrared spectrum of CNAPO in this
region shows three weak bands at 3261, 2959 and
2
1
corresponds to the 3340 cm band in the solid phase
spectrum and is due to intermolecularly hydrogen
2
1
2719 cm (see Fig. 6). It seems that these bands are
overtones of strong bands at 1638, 1481 and
2
1
bonded N–H10 proton. The band at 3171 cm shows
no intensity change on dilution and corresponds to the
2
1362 cm , respectively.
1
2
1
3
assign this band to the intramolecularly H-bonded
161 cm
band in the solid phase spectrum. We
The CxN stretching frequency band appears at
1
2
about 2200 cm in the infrared and Raman spectra of
CNAPO and D CNAPO as a very strong band. The
N–H proton. The absence of an absorption band at
9
2
shorter wavelengths in the solid phase spectrum (due
to the free NH10 proton) indicates that in the solid
phase all CNAPO molecules are engaged in an
intermolecular H-bonding.
spectral behaviour of this band is very similar to that
observed in the spectra of CNAA [20].
2
4.2.2. 1700–1000 cm region
1
The Raman spectrum of CNAPO and its deuterated
Beside the CH and NH deformation and rocking,
3
2

202
H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
Fig. 6. Deconvoluted infrared spectrum of CNAPO in solid phase.
C–CH and C–CN stretching modes, four bands are
3
solvent frequency shift suggests a bending character
for the vibration of this band. According to our normal
mode analysis suggests that this band is mainly dNH2
(51.8%) and is strongly coupled to nCyC (19.2%) and
expected to be observed in this region in relation to
the chelated ring modes which are attributed to CyO,
CyC, C–C and C–N stretching movements. As a
base for the assignment of these modes we studied
geometry of each vibrational mode and we have
determined the percentage of variation of the
geometrical parameters. The results give the follow-
ing assignation.
nC–N (18.5%). In D CNAPO, this band considerably
2
shifts toward lower frequencies and appears at about
2
1
1517 cm with an increase in its Raman intensity.
The upper frequency shift of this band in solution
2
1
(18 cm ) suggests more stretching character for this
band. According to the DFT calculations, this band is
mainly due to the CyC (30.1%) and C–N (23.1%)
The infrared spectrum of CNAPO in solid phase
2
shows a strong band at 1638 cm and a shoulder at
1
2
1
621 cm . The band at 1638 cm is correlated to
21
1
stretching which is coupled to dND (18.2%) and
2
2
1
the 1716 cm DFT calculated wavenumber, so it is
assigned mainly to the CyO stretching mode (49%)
which is coupled to dNH2 (21%) and nCyC (16%).
nCyO (14.6%). The increase in the Raman intensity
of this band upon deuteration is due to increased
nCyC character of the vibration and strongly supports
The small frequency shift of this band in D CNAPO is
2
the calculated results. It is noteworthy that dNH in
2
2
1
in close agreement with the theoretical calculations.
APO appears at 1610 cm , which occurs at lower
frequencies than the corresponding band in CNAPO
21
(1621 cm ). The situation for the deuterated species
2
The shoulder band at 1621 cm in the solid phase
1
2
appears as a strong band at 1605 cm in solution, this
1

H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
203
Table 3
2
Fundamental band assignment of CNAPO. Frequencies are in cm and intensities are relative
1
a
Theoretical
Infrared
Solid
Raman
Solid
Assignment
Frequency RI, I
RI, I
CHCl
3
b
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
3695
3370
3177
3171
3118
3114
3060
3057
2320
1716
1660
1532
1519
1503
1497
1490
1458
1433
1418
1303
1264
1099
1075
1055
1045
1016
924
22
30
63
33
14
43
28
25
59
100
98
5
3340(s)
3362(s)
nNH10(76%) þ nNH
9
(21%)
3161(ms)
3017(w)
3017(w)
2973(vw)
2973(vw)
2928(w)
2928(w)
2200(s)
3171(ms)
3021(vw)
3021(vw)
2974(w)
2974(w)
2935(w)
2935(w)
2204(s)
3200(2)
3023(1)
3023(1)
2975(1)
2975(1)
2930(13)
2930(13)
nNH
9
(77%) þ nNH10(19%)
0.5
n
n
n
n
n
n
a
a
a
a
CH
3
(in plane) (92%)
2
CH
CH
CH
3
3
3
(in plane) (92%)
1
(out of plane) (92%)
(out of plane) (92%)
2
0.2
2
s
CH
CH
3
(97%)
(97%)
s
3
18
2199(100) nCxN(91%)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
42
100
29
4
1638(vs)
1621(sh)
1417(sh)
1481(s)
1642(s)
1644(6)
1616(8)
1419(sh)
1488(9)
1432(sh)
1454(7)
1424(6)
–
nCyO(49%) þ dNH
2
(21%) þ nCyC(16%)
7
1605(s)
dNH
2
(52%) þ nCyC(19%) þ nC–N(19%)
10
7
1424(m)
1480(s)
nCyC(25%) þ dNH
2
(27%) þ nC–C(15%) þ d
a
CH
3
(31%)
d
d
d
d
d
a
a
a
a
a
CH
CH
CH
CH
CH
3
3
3
3
3
(81%)
(87%)
2
11
20
8
1433(w)
1458(sh)
1425(sh)
1382(w)
1372(sh)
1362(s)
1430(w)
1460(sh)
1427(sh)
1387(sh)
1379(m)
1364(s)
19
7
(51%) þ dNH10(39%)
(81%)
0.1
2
(41%) þ dNH
2
(21%)
(20%) þ nC–C(10%)
1
6
8
1373(8)
1361(sh)
1286(9)
1234(11)
1068(6)
dNH
CH
nC–C(29%) þ dNH
2
(46%) þ d
s
CH
3
5
d
s
3
(80%)
40
5
1281(s)
1286(s)
9
(17%) þ nCyC(17%) þ d
s 3
CH (20%)
0.1
8
1237(m)
1243(w)
nC–CxN(29%) þ rNH
2
(24%)
0.2
1
2
1067(mw) 1070(m)
rNH
2
(36%) þ rCH
3
(32%)
0.5 1027(m)
1037(mw) 1029(0.3)
1018(mw) 1011(0.1)
pCH
3
(74%)
3
(78%)
2
1
1
1
1
1
9
1
1
1
2
3
1
1
2
3
1
1010(sh)
990(mw)
914(m)
831(m)
809(m)
669(ms)
638(ms)
595(ms)
547(m)
527(ms)
475(mw)
434(w)
n.m.
pCH
rCH
1
994(m)
910(ms)
p
991(4)
916(4)
836(1)
806(1)
671(82)
638(1)
593(6)
545(18)
528(13)
475(14)
432(1)
402(30)
389(35)
383(sh)
244(11)
223(14)
187(49)
155(13)
n.m.
3
(45%) þ rNH
3
2
(23%)
5
nC–CH
(25%) þ rCH
(38%) þ dCyC–C(21%)
9
(83%)
3
(28%) þ rNH
2
(11%)
3
n
a
C–CH
gNH
3
832
11
p
673
2
660(m)
643(m)
596(ms)
544(sh)
533(s)
480(w)
432(w)
n.m.
D(37%) þ rCH
3
(14%) þ dCxN(13%)
658
1
G(44%) þ gC–CH
D(35%) þ dC–CH
G(55%) þ gC–CH
3
3
3
(27%)
601
1
(19%)?dC–CxN(20%)
(23%)
553
1
548
1
D(46%) þ dC–CxN(14%) þ dC–CH
3
(10%)
534
3
G(49%) þ gC–CxN(28%)
463
0.2
D(60%) þ dC–CH
3
(21%)
424
29
gNH10(72%)
401
1
n.m.
n.m.
D(54%) þ dCxN(14%)
nNHO(38%) þ dC–CH
381
1
n.m.
n.m.
3
(20%)
246
1
n.m.
n.m.
D(38%) þ dC–CH (17%) þ dC–CxN(10%)
3
201
0.05
2
0.2 n.m.
n.m.
0.2 n.m.
n.m.
G(48%) þ gC–CxN(18%) þ gC–CH
dC–CxN(33%) þ D(20%) þ dC–CH
G(48%) þ gC–CxN(17%) þ gC–CH
tCH (78%)
gC–CH
(27%) þ G(27%) þ gC–CxN(23%)
tCH (89%)
3
(17%)
157
3
n.m.
3
(13%)
148
0.02
n.m.
3
(12%)
110
,0
2
,0
,0
n.m.
n.m.
n.m.
3
86
n.m.
n.m.
3
53
0.1
0.8 n.m.
n.m.
n.m.
3
IR, infrared; R, Raman; I, calculated relative intensity; n, stretching; d, in plane bending; g, out of plane bending; r, rocking in plane; p,
rocking out of plane D, in plane ring deformation; G, out of plane ring deformation; v, very; s, strong; m, medium; w, weak; sh, shoulder; t,
torsion; n.m., not measured; p , solvent overlapped, relative intensities are given in parentheses.
a
p
Unscaled Frequencies, Calculated at B3LYP/6-31g (p added on amine protons) level.
b
For the DFT assignment means the percentage of deviation of the bond stretching and bond angle.

204
H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
Table 4
21
2
Fundamental band assignment of D CNAPO. Frequencies are in cm and intensities are relative
a
Theoretical
Infrared
Solid
Raman
Solid
Assignment
Frequency
RI, I
RI, I
CHCl
3
b
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
3177
3171
3118
3114
3060
3057
2726
2481
2320
1710
1585
1521
1503
1498
1490
1479
1437
1419
1308
1241
1126
1075
1065
1055
1015
933
1
4
14
43
28
51
60
99
26
14
100
5
3017(vw)
3017(vw)
2974(w)
2974(w)
2929(w)
2929(w)
2490(ms)
2330(ms)
2200(s)
1632(vs)
1517(ms)
1480(mw)
1433(sh)
1440(s)
1422(sh)
1400(mw)
1381(mw)
1362(ms)
1287(s)
1217(m)
1074(w)
1027(m)
1037(sh)
1009(sh)
926(m)
834(m)
846(sh)
655(m)
676(ms)
591(ms)
510(ms)
543(m)
525(ms)
448(w)
414(w)
n.m.
3020(vw)
3020(vw)
2975(w)
2975(w)
2935(w)
2935(w)
2510(s)
2351(ms)
2204(s)
1638(s)
1535(m)
1481(sh)
1430(sh)
1439(ms)
1420(sh)
1411(m)
1379(m)
1363(m)
1291(s)
1220(sh)
1070(w)
1037(w)
1030(sh)
1018(w)
917(ms)
p
3022(2)
3022(2)
2976(2)
2976(2)
2929(18)
2929(18)
2506(3)
2353(4)
2196(100)
1638(6)
1525(13)
1487(1)
1431(sh)
1437(8)
1418(6)
1400(3)
1375(5)
1359(3)
1282(8)
1213(1)
1080(1)
1029(sh)
1041(5)
1012(0.2)
928(2)
n
n
n
n
n
n
a
a
a
a
CH
CH
CH
CH
3
3
3
3
(in plane) (89%)
(in plane) (89%)
2
(out of plane) (90%)
(out of plane) (91%)
3
1
s
CH
CH
3
(96%)
(97%)
4
s
3
25
28
28
88
100
5
nND10(76%) þ nND
9
(17%)
nND
nCxN(89%)
9
(82%) þ nND10(14%)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
nCyO(59%) þ nCyC(17%)
nCyC(30%) þ nC–N(23%) þ nCyO(14%) þ dND
12
6
2
(18%)
d
d
d
d
a
a
a
a
CH
CH
CH
CH
3
3
3
3
(89%)
3
10
3
(87%)
26
2
(71%) þ nC–N(11%)
6
(79%)
50
27
4
nCyC(26%) þ nC–C(18%) þ dND
2
(15%) þ d
a 3
CH (29%)
0.5
d
d
s
CH
CH
3
(77%)
(76%)
8
51
7
7
s
3
6
nC–CxN(32%) þ nC–CH
3
(28%)
2
nC–C(36%) þ dND
9
(27%) þ nCyC(15%)
10
2
2
dND
pCH
2
(47%) þ rCH
3
(33%)
1
3
(73%)
2
2
rCH
pCH (70%)
3
3
(38%) þ dND
2
(37%)
2
1
3
1
nC–CH
3
(29%) þ rCH
(34%) þ dCyC–C(21%) þ dND10(19%)
(77%)
G(52%) þ ?gC–CH
D(39%) þ dC–CH (20%) þ dCxN(10%)
D(30%) þ dCxN(22%) þ dC–CH (14%)
gND (59%)
G(53%) þ gC–CxN(26%)
D(45%) þ dC–CH (12%) þ dC–CxN(11%)
G(52%) þ gC–CxN(24%)
(17%)
3
2
(36%) þ dND (12%)
6
1
835(3)
n
a
C–CH
3
864
0.2
0.3
p
844(3.5)
659(70)
675(sh)
589(12)
509(1)
rND
2
686
6
0.1
9
655(w)
671(m)
590(m)
506(m)
544(m)
518(m)
449(m)
417(sh)
n.m.
3
(20%)
660
4
3
595
2
1
3
586
3
1
9
548
1
1
543(18)
522(2)
545
1
2
3
521
4
2
447(1)
437
0.5
1
1
414(1)
D(65%) þ dC–CH
3
399
2
387(24)
365(28)
313(1)
D(53%) þ dCxN(14%)
nNDO(34%) þ dC–CH
gND10(51%)
362
2
3
n.m.
n.m.
3
(21%)
325
24
0.1
0.3
0.1
3
n.m.
n.m.
242
2
n.m.
n.m.
239(13)
218(16)
189(35)
152(2)
D(42%) þ dC–CH
G(44%) þ ?gC–CH
dC–CxN(34%) þ D(20%) þ dC–CH
G(48%)? þ gC–CxN(16%) þ gC–CH
tCH (78%)
G(28%) þ ?gC–CH
tCH (89%)
3
(16%) þ dCxN(9%)
(19%) þ gC–CxN(18%)
(10%)
(12%)
195
0.5
3
n.m.
n.m.
3
157
n.m.
n.m.
3
146
0.1
0.2
0.1
n.m.
n.m.
3
109
,0
3
n.m.
n.m.
n.m.
3
86
0.03
1
n.m.
n.m.
n.m.
3
(26%) þ gC–CxN(23%)
53
0.1
n.m.
n.m.
n.m.
3
IR, infrared; R, Raman; I, calculated relative intensity; n, stretching; d, in plane bending; g, out of plane bending; r, rocking in plane; p,
rocking out of plane D, in plane ring deformation; G, out of plane ring deformation; v, very; s, strong; m, medium; w, weak; sh, shoulder; t,
torsion; n.m., not measured; p , solvent overlapped, relative intensities are given in parentheses.
a
p
Unscaled frequencies, calculated at B3LYP/6-31g (p added on amine protons) level.
b
For the DFT assignment means the percentage of deviation of the bond stretching and bond angle.

H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
205

206
H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
is vice versa, the corresponding wavenumber in APO
occurs at higher frequencies than that for CNAPO.
This fact can be easily interpreted as follows: for the
to nC–CyC–N [11]. The change in the vibrational
mode of this band could be attributed to the more band
equalization in the chelated ring due to the stronger H
bond in CNAPO than that in APO. According to the
light species the vibration is mainly dNH , therefore
2
p
we expect the band appear at higher frequencies in
CNAPO than that for APO, but in the deuterated
species this band is mainly nCyC and we expect to
observed the band at lower frequencies in CNAPO
than that in APO because of more p-delocalization
due to the more conjugated hydrogen bond assisted,
RAHB [18,35].
ab initio calculations (at B3LYP/6-31G level), the
C –C and C –C distances in CNAPO are longer
2
3
3
4
˚
than those in APO (0.023 and 0.021 A, respectively)
but the C –N distance is shorter in CNAPO than the
4
8
˚
corresponding bond length in APO (0.013 A). An
increase in the frequency of this band by going from
solid to solution also suggests that this band has
mainly a stretching character. The corresponding
band in the deuterated analogue is coupled to the ND9
in plane bending mode, which explains the frequency
shift upon deuteration.
2
1
The band at about 1420 cm appears as a shoulder
in the Raman and infrared spectra of CNAPO. This
band upon deuteration shows a low frequency shift
2
1
(
about 18 cm ), which is in close agreement with the
theoretical calculations. By considering the DFT
calculations, this band is assigned to the CyC and
C–C stretching modes coupled to dNH and dCH .
Infrared and Raman spectra of CNAPO show a
2
1
band at about 1235 cm . According to the theoretical
calculations, this band is ascribed to the coupled mode
nC–CN þ dNH . Upon deuteration, this band shifts
2
3
On the other hand, theoretical calculation shows that
the frequency shift upon deuteration is due to
decoupling of CyC and C–C stretching and NH in
1
0
2
1
about 50 cm upwards and its coupling to dNH is
1
0
completely removed. These observations are in
agreement with the theoretical calculations. Decou-
pling of dNH10 from C–CN stretching explains the
upward frequency shift upon deuteration. The corre-
sponding band in CNAA [20] also shows an upward
2
plane bending motions. In addition, deuteration
causes an increase in the intensity of this band in the
infrared spectrum because of more nCyC and nC–C
characters in the deuterated analogue compared with
the light compound. The Raman spectrum of CNAPO
2
1
frequency shift of about 65 cm upon deuteration.
By considering the theoretical calculations and
comparing with the spectra of APO [11], CNAA [20]
and acetylacetone [36], the bands at about 1481, 1433,
2
1
shows a medium band at 1373 cm . The correspond-
ing IR band appears as a shoulder and upon
deuteration disappears. According to the theoretical
calculations, this band is mainly due to the NH2
deformation (45.7%), which is somewhat, coupled to
other chelated ring atom movements and symmetric
CH3 deformation mode (20.3%). In the case of
D CNAPO this mode is coupled mainly to the rCH
2
1
1425 and 1362 cm
deformation modes.
were assigned to the CH3
2
1
4.2.3. Below 1000 cm
In this region one expects to observe C–CH3
stretching, C–CH3 and C–CN bending and ring
deformation modes.
2
3
(
at around 1040 cm . Another strong IR band in this
38.4%) and appears, as it is predicted by calculations,
21
2
1
region is a band at about 1280 cm . The correspond-
ing Raman band appears as a medium band at
The infrared and Raman spectra of CNAPO
2
1
indicate a band at about 990 cm , which disappears
upon deuteration. By considering the theoretical
calculations, we assign this band to rNH , which is
2
1
1
286 cm . By the help of the theoretical calculations
and intensity considering we assign this band to C–C
28.8%) and CyC (17%) stretching modes coupled to
N–H in plane bending mode (16.6%) and d CH
3
2
(
coupled to rCH . Theoretical calculations suggest
3
2
1
that the band at about 914 cm is due to nC–CH3
(25.3%) which is coupled to rCH (27.8%) and rNH
(11.2%). Upon deuteration, this band shows an
9
s
(
goes a large frequency shift and appears as a weaker
20.1%). In the case of D CNAPO this band under-
2
3
2
2
band at about 1215 cm . The corresponding band in
1
21
upward frequency shift of about 12 cm . The
21
corresponding band in APO (980 cm ) [11] shows
2
1
APO also shows a downshift of about 20 cm upon
deuteration. It should be mentioned that this band in
APO and its deuterated analogous is assigned mainly
2
1
also an upward frequency shift (11 cm ) upon
deuteration. According to the theoretical calculations,

H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
207
2
we assign the band at 926 cm in D CNAPO to nC–
1
5. Conclusion
2
CH , which is coupled to dND and rCH . The
3
2
3
2
1
infrared band at 831 cm
shows an upward fre-
CNAPO was synthesized by reaction between
a-cyanoacetylacetone and ammonia. The Fourier
quency shift upon deuteration, which is in close
agreement with our theoretical calculations. Accord-
ing to the calculations, we assign this band to the
2
1
transform infrared spectra from 3500 to 400 cm of
the solid and solution and the Fourier transform
2
1
asymmetric C–CH stretching mode (37.8%) coupled
3
Raman spectra from 3500 to 150 cm for the solid
have been recorded for CNAPO and its deuterated
analogue. A vibrational assignment is proposed based
on the ab initio predicted frequencies, relative
intensities of both spectra and frequency shift upon
deuteration. All theoretical calculations and exper-
imental results reveal a stronger intramolecular H-
bond by CN substitution in the a-position of APO
than that in APO. This result is consistent with that
obtained for acetylacetone.
to the in plane CyC–C bending mode (21.3%).
The infrared and Raman spectra of CNAPO
2
1
indicate two bands at about 809 and 402 cm
which completely disappear in D CNAPO spectra.
,
2
According to our calculations, these two bands are
caused by gNH and gNH , respectively. In the case
9
10
of APO, the latter is strongly coupled to gCH but the
a
2
1
former appears at lower frequencies (755 cm ) than
2
1
that for CNAPO (809 cm ). This frequency shift also
supports the presence of stronger hydrogen bond in
CNAPO compared to that in APO and very well
agrees with the NMR proton chemical shift.
Theoretical calculations show that both hydrogen
of the NH groups are in the plane of the chelated ring.
2
Analysis of the vibrational spectra indicates strong
coupling between the chelated ring modes.
It is noteworthy that the frequencies of the in plane
ring deformation modes in CNAPO are considerably
higher than the corresponding modes in APO. This
could be attributed to the stronger ring in CNAPO in
comparison with APO, which is caused by stronger
hydrogen bond and more p-electron delocalization in
References
2
1
[
1] K. Ueno, A.E. Martell, J. Phys. Chem. 59 (1955) 998.
the former. The 620 cm band in APO appear at
2
1
21
[2] N.H. Cromwell, Chem. Rev. 38 (1946) 83.
6
69 cm in CNAPO and the 462 cm band in the
former splits to two bands in the latter at 527 and
[
[
3] H.F. Holtzclaw, Jr., J.P. Collman, R.M. Alire, J. Am. Chem.
Soc. 80 (1958) 1100.
2
95 cm . Coupling of this in plane ring deformation
1
5
4] G.O. Dudeck, E.P. Dudeck, J. Am. Chem. Soc. 86 (1964)
4283.
to the C–CxN in plane bending mode causes this
splitting.
It is interesting to consider the frequency shift of
[5] G.O. Dudeck, G.P. Volpp, J. Am. Chem. Soc. 85 (1963) 2697.
6] G.O. Dudeck, R.H. Holm, J. Am. Chem. Soc. 84 (1962) 2691.
[7] G.O. Dudeck, E.P. Dudeck, J. Chem. Soc. (B) (1971) 1356.
[
2
1
out of plane ring deformation mode at 638 cm upon
deuteration. This frequency shift is caused by
coupling of this mode with gNH/gND and is predicted
correctly by the theoretical calculations. The medium
[
[
8] D.L. Ostercomp, J. Org. Chem. 30 (1965) 1169.
9] J. Dabrowski, J. Terpinski, Tetrahedron Lett. 19 (1965) 1363.
[
10] S.F. Tayyari, F. Milani-nejad, M. Fazli, J. Mol. Struct.
(Theochem) 541 (2001) 11.
2
1
infrared and Raman band at about 547 cm corre-
sponds to another out of plane ring deformation mode.
The theoretical calculation predicts that this band
[11] S.F. Tayyari, H. Raissi, F. Tayyari, Spectrochim. Acta 58A
2002) 1681.
(
[
12] S.F. Tan, K.P. Ang, H.L. Jayachandran, A. Jones, W.R. Begy,
J. Chem. Soc. Perkin Trans. 2 (1982) 513.
2
1
shifts about 5 cm
D CNAPO, which is in close agreement with the
toward lower frequencies in
[
13] P.E. Hansen, S. Bolving, T. Kappe, J. Chem. Soc. Perkin
Trans. 2 (1995) 1901.
2
experimental observations.
The N· · ·O stretching mode in the APO spectrum at
[14] G. Klebe, in: H.B. Burgi, J.D. Dunitz (Eds.), Structure
Correlation, vol. 2, VCH, Weinheim, 1994, p. 453.
[15] G.A. Jeffery, W. Sanger, Hydrogen Bonding in Biological
Structure, Springer, Berlin, 1991.
2
60 cm also shows considerable upward frequency
1
3
2
1
shift (383 cm ) by CN substitution in the a-position.
This frequency shift also supports the presence of
stronger hydrogen bond in CNAPO compared to that
in APO.
[
16] W. Saenger, Principle of Nucleic acid Structure, Springer,
New York, 1984.
[
17] D.L. Rowland, L. Myers, A. Culver, J.M. Davidson, J. Clin.
Psychopharmacol. 17 (1997) 350.

208
H. Raissi et al. / Journal of Molecular Structure 613 (2002) 195–208
[
[
[
[
[
[
[
18] V. Bertolasi, P. Gilli, V. Ferretti, G. Gilli, J. Chem. Soc. Perkin
Jr., R.E. Stratmann, J.C. Burant, S. Dapprich, J. M Millam,
A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi,
V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C.
Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala,
Q. Cui, K. Morokuma, D.K. Malick, A.D. Rabuck,
K. Raghavachari, J.B. Foresman, J. Cioslowski, J. V. Ortiz,
B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi,
R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham,
C.Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe,
P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres,
C. Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople,
GAUSSIAN 98, Revision A.3, Gaussian, Inc., Pittsburgh, PA,
Trans. 2 (1997) 945.
19] Z. Yoshida, H. Ogoshi, T. Tokomitsu, Tetrahedron 26 (1970)
5691.
20] S.F. Tayyari, H. Raissi, F. Milani-nejad, I.S. Butler, Vib.
Spectrosc. 26 (2001) 187.
21] J. Emsley, L.Y.Y. Ma, S.C. Nyburg, A.W. Parkins, J. Mol.
Struct. 240 (1990) 59.
22] J. Emsley, L.Y.Y. Ma, P.A. Bates, M. Motevalli, M.B.
Hursthouse, J. Chem. Soc. Perkin Trans. 2 (1989) 527.
23] J. Emsley, L.Y.Y. Ma, S.A. Karaulov, M. Motevalli, J. Mol.
Struct. 216 (1990) 143.
24] J. Emsley, N.J. Freeman, P.A. Bates, M.B. Hursthouse,
J. Chem. Soc. Perkin Trans. 1 (1988) 297.
1
998.
[
[
[
[
32] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
[
[
25] G. Buemi, F. Zuccarello, Electr. J. Theor. Chem. 2 (1997) 302.
26] K.L. Wierzchowski, D. Shugar, Acta Biochim. Polon. 7 (1960)
33] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 875.
34] P.M.W. Gill, Mol. Phys. 89 (1996) 443.
63.
35] V. Bertolasi, P. Gilli, V. Ferretti, G. Gilli, J. Am. Chem. Soc.
[
27] K.L. Wierzchowski, D. Shugar, A.R. Katritzki, J. Am. Chem.
1
13 (1991) 4917.
36] S.F. Tayyari, F. Milani-nejad, Spectrochim. Acta 56A (2000)
681.
Soc. 85 (1963) 827.
[
[
[
[
[
28] J.P. Fackler Jr., F.A. Cotton, Inorg. Chem. 2 (1963) 102.
29] J. Weinstein, G.M. Wyman, J. Org. Chem. 23 (1958) 1618.
30] H. Raissi, PhD Theses, Ferdowsi University, Mashhad Iran,
2
37] C.A. T e´ lles, E. Hollauer, M.I. Pais da Silva, M.A. Mondrag o´ n,
I. Haiduc, M. Curtui, Spectrochim. Acta 57A (2001) 1149.
38] A.R. Katrizky, R.A. Jones, J. Chem. Soc. (1959) 3674.
39] A. Gardner, A.R. Katritzky, J. Chem. Soc. (1957) 4375.
2001.
[
[
[
31] M.J. Frisch, G.W. Trucks, H.B. Schlegel, F.E. Scuseria, M.A.
Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A.G. Montgomery